Adjustable transformer



July 1l; 1944. c. P. BOUCHER 2,353,542

' ADJUSTABLE TRANSFORMER Filed Nov. 10:., 1939 2 Sheets-.Sheet 1 fichi@`July 11,1944. c. P.'BouvcH|-:R v 2,353,542

ADJUSTABLE TRANSFORMER Filed Nov. 10, 1939 2 Sheets-Sheet 2 f fF`-"*Il-, ik?. 7,

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Patented July 11, 1944 ADJUSTABLE TRANSFOBMER Charles Philippe Boucher,Paterson, N. J., assignor to Boucher Inventions, Ltd., Washington,A D.C., a corporation of Delaware Application November 1o, 193s, serial No.303,886

4 claims. (ci. 1v1- 119) ings, Figure 1 is a schematic front elevationMy invention relates to the operation of iluorescent, luminous gasdischarge tubes and to transformer apparatus for operating such tubes.

An object of my invention is to produce a method of operating, inextremely simple and highly emcient manner, fluorescent, luminous gasdischarge tubes, so as to produce a mellow light of satisfactorybrilliance, which is free of stroboscopic effect, and which can bemaintained `at substantially constant intensity of light emissionthroughout the useful life of the tubes.

Another object is to produce a method of operating such tubes which ischaracterized .by thehigh light emission per unit `of energy input, thelow operating costs attendant upon the use of the method, the avoidanceof danger of overloading the power equipment, and the realizatioxi ofthe desired results with but a minimum of modification of existingequipment.

Another object is to produce a silently operating, substantiallyfool-proof system of one or more fluorescent, luminous gas dischargetubes simple, and durable, comparatively inexpensive, high voltagetransformer equipment, and which system is' characterized by the cooloperation of the tubes, the'long life oi' the component parts of thesystem, the markedly increased light emission per unit of energy input,and the simplicity of all electrical connections employed; vand whichsystem possesses marked flexibility, being adaptable to substantiallyany reasonable size or configuration of tubing desired.

Still another obect is to produce a new constant current transformerforuse with negative loads,. which is characterized by its simplicity,durability, long life. and low invest- `and their energizing equipment,acceptable to -the Fire Underwriters, and employing extremely view andFigure 2 a corresponding side elevation view of a transformer and tubeassembly embodying my invention.

Figures 3, 4 and 5 are fragmentary front elevations showing details ofseveral forms of magnetic by-epasses for transformers according to myinvention.

Figure 6 is a detail of an embodiment of my invention, wherein the'air-gap of the magnetic by-pass for-the transformer .is bridged by arotor, rotatable to vary the effective dimensions of the air-gap. y A

Figure 'I shows in elevation the details of a swingable bridging member,while Figures 8 and 9 are corresponding end and front elevations of anembodiment wherein a strip of magnetic material is used to bridge somuch of the air-gap of the magnetic by-pass as is desired.

Like reference characters. denote like parts throughout lthe severalviews of the drawings.

As conducive to a more thorough understanding of my invention, it may benoted that for a number of years, illuminating engineers have reliedupon the nitrogen-filled, tungsten illament electric light bulb as byfar the principal source of artificial light. -This light source gives avery satisfactory white light of considerable brilliance. It is found,however, that the major portion of the electrical energy input to suchbulbs is dissipated in the form of heat. This is conservativelyestimated as being ment both initially and in maintenance.- and whichcan be adjusted at will and with great semitiveness to produce a desiredmaximum current flow in the transformer secondary winding, up to theultimate maximum current-carrysalt, well known in the art, and theparticular tvoe of which largely determines the color and quality of theradiation emitted. The salt is energized from any suitable source ofradiant energy, such, for example, as a mercury vapor arc. Y Theradiation emanating interiorly of the Vtube from the glow or diffusedarc discharge occurring through the mercury vapor or other suitable'gas,although perhaps of wave-length too short to register on the naked eye,strikes lconverted into against and energizes the fluorescent salt.These salts, thus excited, then give rise to a steady continuousradiation of visible mellow light characteristic to the particular saltor combination of salts used. A tube thus operated is found to run cool,and inasmuch as its emission is continuous, there is a total absence ofobjectionable flicker, known as stroboscopic effect, such as inencountered where the light-emitting source is energized directly froman alternating current source. 'Ihus the flicker, noticeable when anordinary bare mercury arc lamp or a tungsten lament bulb is energized bya 60 cycle current source and particularly objectionable when a 25 cycleenergizing source is employed, and which has a frequency of 1,420 or17%,() of a second, respectively, is completely avoided. Such tubes arefound to have a light-emitting eiiiciency many times that of theordinary incandescent lamp or, in other words, their light emission rperunit of energy input is much greater than that of the conventionaltungsten filament lamp. In'point of fact, such uorescent White light hasbeen found to be the most economical source of artificial white lightknown, so far as concerns power consumption.

Because of these marked advantages, fluorescent tubes are employed notonly in commercial and industrial installations, but have recently comeinto rather widespread use in household, store, and other interiorlighting. Such tubes have recently been developed for operation atordinary household voltages, such as 110 and 220 volts.

It has been found that, while the emciency of light emission from suchtubes is great, the bril- Iiancy or total emission of light is notnearly so large as that of filamentary lamps. Accordingly it has becomethe practice to operate these tubes in multiple, to build up the totallight emission to the required value.

A ilxture is provided for receiving these tubes, and the tubesthemselves are handled and sold as are ordinary electric bulbs. When theuseful life of the tube is terminated, it is simply replaced in thefixture. I find that these tubes produce an average of 30 to 40 lumensper watt input, for the extent of their useful life, which, whenoperating under favorable conditions, is about 2000 hours.

Certain disadvantages have been encountered in the practical utilizationof low voltage fluorescent tubes. In the arrangement of such tubelighting now in use, one disadvantage is a high initial cost ofequipment. It has been found that a 110 volt potential will energize nomore than about 24 inches of tubing. Where such a tube is connecteddirectly to household mains, a current limiting device must be used foreach 24 inch section of tubing, a resistor being commonly used for thispurpose. Furthermore, a heater must be provided for each unit to bringthe mercury filling to a point where an arc can be struck at ll volts.Thus, if a tube 6 feet in length is desired, it is obvious that the tubemust be laid into sections no more than 24 inches in length and that foreach section resistors, heaters, and current-carrying electrodes must beprovided.

Furthermore, it has been observed that after fluorescent tubes have beenin operation for some l0 to l5 light hours, their original brilliancydiminishes materially, or, in other words, their light emission for aconstant energy input decreases considerably. This condition ofdiminished brilliancy continues at about a constant level for some time,about two thousand light Ycost of maintenance and replacement.

hours, when a further-decrease in unit light emission is encountered.This nnal decrease necessitates replacing the tube by a fresh one. Onepossible explanation for this phenomenon of decreasing brilliancy isthat it is due to deteriorationoi the fluorescent salts with which theinner wall of the tube is coated, but the exact nature of thisoccurrence is not now known so far as I am aware.

The decrease in emission of light and consequent early discarding of thetubes cause a high Because of the importance of this element of cost,the introduction of such tubes into new fields of illumination has notbeen quite so widespread as it would otherwise be, particularly in thecase of those tubes designed and constructed for operation at lowvoltages.

The greatest disadvantage of these tubes is experienced when it becomesnecessary to replace them in operation. When a tube is discarded, withit must be discarded the electrodes and heaters. Where a pair ofelectrodes, a heater, and a current-limiting device are provided everytwenty-four inches, it will readily be appreciated that the investmentdiscarded upon scrapping a tube is relatively high.

Another disadvantage of these tubes for lowvoltage use is that, inrequiring complicated installations of heaters, current-limitingdevices,

and electrodes, the service charges for installing them are high sinceonly skilled labor can satisfactorily carry out the operational stepsrequired.

An important object of my invention, therefore, is to produce a systemof fluorescent, luminous gas discharge tube energizing equipment, and amethod of operating the same in simple, efficient and economical manner,at high voltages, with long llife and with constant intensity of lightemission, in which the cost of replacing the parts thereof is low, whichentails a minimum expenditure for labor in installation and maintenance,and which is entirely acceptable to the Fire Underwriters.

Despite the disadvantages pointed out in the foregoing, it appears, asalready pointed out, that fluorescent tubes are becoming more and moreused for illumination purposes, displaying a strong tendency to replaceordinary incandescent lighting systems. Their efficiency, mellow light,and low temperature of operation make their use advantageous, so that itis most desirable that a system using these tubes be designed in which aconstant emission of light, long life, and steady operation areobtained.

It may be stated in general that one of the objects of my invention canbe accomplished by operating the fluorescent tube or tubes atcomparatively high voltage, and by increasing the current input to thetube as the light emission thereof per unit of power input decreases, insuch manner, and in such proportion to the said unit decrease of lightemission, that the total light emission from the tube is maintainedsubstantially constant.

As illustrated in general in Figure l, my invention comprises a new formof constant-current transformer, and a system consisting of such atransformer and a negative load therefor. My

invention also comprises a method of operating such system. Thetransformer' includes a core having legs Ill, II, I2 and I3, forming aclosed path. Primary coil section I4 is mounted on leg I0, whilesecondary coil sections I5 and IE are mounted on leg l2. Straps I1 andI8 conveniently are provided, preferably of paramagnetic tion.

material, such as steel, for securing the laminations of the core partsagainst chattering.

Primary winding Il is connected by suitable leads I9, to a source 2I ofsingle-phase alternating current electrical energy, such as the usual110 volt or 220 volt commercial source.

The secondary coil sections II and I6 are connected together in seriesby way of conductors 22 and 23. The two coil sections thus forming thesecondary winding are connected by way of conductors and 2B to thefluorescent luminous gas discharge tube 21 or other load. In order thatthe potential to ground shall not exceed a value permitted by the FireUnderwriters,l and yet maximum voltage be available for tube energization, the interconnections between coil sections, that is conductors22 and 23, are connected to 'core I2 which in turn is grounded as at 2l.

The luminous tube 21 comprises an elongated piece of glass tubing,coated on its interior wall with a suitable fluorescent salt. The tubeis of proper length and configuration to produce the desiredillumination. Simple and conventional electrodes of suitable type areprovided, one at each end of the tube. Since the brilliancy ofillumination of these tubes is found to vary inversely with theircross-sectional diameter, I prefer to -form them from small diametertubing. It will be appreciated that one important advantage of lthe useof such tubing, as compared with other low voltage tubes recently madeavailable for use, is their extreme simplicity, making it possible foranyone equipped to produce the conventional neon tubes, to manufacturethese fluorescent tubes with but little if any additional equipment, andthis of a very simple and inexpensive type.

While the load has been shown as comprising a single tube 21, it is ofcourse, apparent that it may comprise any number of tubes `connectedeither in series or in parallel. Moreover the secondary coil sectionsI5, I 6 can be connected to the load either in series, as illustrated inthe drawings, or in parallel, depending upon whether the coil sectionsthemselves are so related to each other and to the core as to be inseries-aiding or in series-opposition (bucking) An important requirementof the transformer according to my invention is that it be provided witha magnetic shunt path to limit the current output of the secondary coilsections. In practice my transformer is designed and calibrated for acertain maximum secondary current output, and this output is limited bythe shunt. Such shunt employs one or more magnetic .flux by-passeshaving a predetermined reluctance.

Usually these by-passes include one or more gap is employed, I procureeffective control of air-gaps.l The construction preferably is such thatnothing can cause the transformer secondary winding to develop a currentin excess of the maximum rated secondary current. 'I'his means, where amagnetic by-pass having a fixed air-gap is employed, that the shuntpreferably should be integral with the core proper and the air-gapmechanically set. These shunts may be disposed either externally orinternally of the secondary coil sections. By that I mean that the shuntabout a secondary coil section is disposed either externally orinternally of the outer conflnesof the main core of the transformer. Inthe instance of a transformer of internal shunt construction, provisionis made for means extending externally of the casing, for manipulationof the shunt in accordance with my inven- At the present time, I believethe external shunt to be more practical in connection with my invention,and such an external shunt is illustrated in the transformer of Figuresland 2. However, I do not desire to be bound by my present preferencefor the use of external shunts, for it may well be that furtherinvestigation will demonstrate that internal shunts, such as thoseillustrated in the transformers of Figures 8 and 9, are of equaladvantage in connectionwith my invention.

Considering more particularly the core construction, leg I2 preferablyis provided, as shown in Figure l, with a substantially T-shaped coreextension 28, having heads 28a and 2th. This T-shaped extensionprotrudes outwardly from leg I2, between and beyond the secondary coilsections II, Il. The heads 28a, 2lb extend laterally from the center legof core extension 2l, substantially parallel with and in spaced relationto the leg'l2. Similarly, legs II and I3 are, provided with extensionsIIa and Ila, preferably of reduced cross-section. These last-mentionedextensions protrude beyond the symmetrical confines of the core from thesame end thereof and in the same direction as protrudes the coreextension 2l. The extensions IIa and Ita extend closely adjacent to butseparated from heads 20s,.

2lb, respectively, by the short air-gaps GI and G2.

'I'he by-passes for the magnetic ux serve to shunt part or all of theflux coursing the main core around the secondary coil sections, theairgaps included in the by-passes limiting this shunting action. It willbe evident that in general,

upon decrease in the reluctance of the by-pass,v

= tained such that practically no current can flow through the secondarycoil sections. For such adjustable control, adjustable partial bridgingof the air-gaps is provided. Where no gap is used in the by-pass, thecontrol can be accomplished by providing means for increasing anddecreasing the etlectlve cross-section of the by- Where a shuntconstruction including an airthe air-gap in one of three principalmanners. One of these is to provide a fixed air-gap and provide anadjustable bridge therefor. Another is to vary the length of theair-gap, while yet another is to vary the effective area thereof. Manymodifications in each of these three categories may readily be realized.

In the example of Figures 1 and 2, I employ a fixed, external air-gap.Control of the effective'- ness of the by-pass is obtained by the use ofbridging means in the form of magnetic blocks.

reluctance by-passes, and practically no flux would pass through thecore I2 and very little current would flow through the secondary coilsections. A partial bridging of the air-gaps GI, G2 will bring the valueof the maximum current which can ow in the secondary coil sections to acertain predetermined minimum, sufficient to energize effectively thetube load 21 when the tubes are first installed.

Bridging blocks 29, 30 serve to permit the partial bridging Of theair-gaps included in the shunt paths. Each block preferably is dividedinto a selected number of sections or stacks. In the embodiment shown,referring to FigureZ, there are in each block three stacks 29a, 29h,29C, and 30a, 30D, 3Uc, respectively. The operation of these blocks wil1be described hereinafter.

Since, as has Abeen stated, the effect of the bridging blocks, unlessprecautions to the contrary are taken, is to completely short theair-gaps GI and G2, I nd it advisable to interpose a membrane 3| betweenthe air-gaps and the bridging blocks. This membrane is made of suitablenonmagnetic material, either metallic, or non-metallic, such,forexample, as aluminum, brass, Bakelite, ber, paper or the like. Thus,when intimate contact between the magnetic by-passes and the bridgingblocks is prevented, it is possible for the primary flux to build up avoltage in secondary coil sections I5, I6 suflicient to strike an arcacross tube 21.

My transformer may be of the core and coil type, that is, having nocontainer and no insulating compound and in which the coil terminals arereplaced by flexible leads, or it may be provided with a casing and afilling of suitable insulating compound. In the transformer according toFigures 1 and 2, I prefer to provide a casing 32 having a base 33 and acover 34, all preferably formed of some suitable inexpensive materialsuch as steel or iron. This casing nts snugly about thetransformer, andpreferably has in one side thereof a window 35 i Figure 2) which iscovered by membrane 3I. This membrane may be soldered, spot-welded,riveted (Figure 2), or`

otherwise securely tted to casing 32, as indicated at 36, therebysealing the insulating compound against leakage.

Blocks 29 and 30 preferably are enclosed snugly in small metalcontainers 31, one of which is shown partly broken away over the block29, and which I prefer to make fast to casing 32. These containersprovide a very convenient Way of mounting the blocks, and also serve toprevent undue humming.

In the operation of my transformer, at the first part of a givenhalf-cycle, with flux coursing as indicated by the arrows, the voltageinduced in coil sections I5, I6 is not suicient to strike an arc. Henceno current flows in the coil sections and consequently no magnetomotiveforce opposing the main flux is developed. Therefore,lthe core leg I2forms the path of least reluctance, and most of the ilux courses thisleg interlinking the secondary coil sections. At the moment when theinduced secondary terminal voltage reaches a value sufficient to strikean arc across tube 21, however, the tube resistance drops and a surge ofcurrent occurs through the tube. This current, flowing through coilsections I5, I6, generates a flux tending to flow in a direction counterto the main flux, bucking the main body of flux 'and causing it to seekthe path of least reluctance.

This path is then the magnetic by-pass constituted by leg extension IIa,air-gap GI, head 28a,

head 28h, air-gap G2, and leg extension Ila. Just enough ux courses legI2 to insure development of suflicient voltage in the secondary coilsections to energize tube 21 in its conductive condition.

During the latter part of the half-cycle in question, the value of theflux decreases, until a point is reached where the developed voltage isno longer sufficient to maintain the arc across the tube. The arc thenextlnguishes and current flow stops. Immediately the generation ofcounter flux terminates, and the main body of flux, no longer impeded,resumes its coursing of leg I2.

In the next half-cycle, the direction of coursing of flux is opposite tothat of the arrows. Until the generated voltage reaches the strikingpotential of the tube, the ux courses leg I2, in an upward direction inFigure 1. When the arc is restruck, the counter magnetomotive forcegenerated bucks the main body of flux, forcing the major part to coursethe by-.pass Ha, G2, 28h, 28a, GI and I Ia. Finally, in the latter partof this second half-cycle, the value of flux diminishes until thegenerated voltage is no longer sufcient to maintain the arc discharge,the tube extinguishes, and due to absence of counter magnetomotive forcethe main body of flux again courses leg I2.

Under full short-circuit conditions, a current lbegins to flow in theVsecondary coil sections Il and I6 immediately upon the flux building upin core I2. Back magnetomotive forces are developed in these coilsections from the outset, therefore, which oppose the growth o1' flux incore portion I2. As a consequence, a large lpart of the magnetic iluxtraverses the by-pass or shunt -path IIa, 28a, 28h and I3a provided forthis purpose, this path including the two air-gaps GI and G2. In otherwords, the transformer operates very much as it does under ordinary loadconditions, the current in coil sections I5 and Il being limited to safevalues |by virtue of the shunting of magnetic flux linking these coilsections as noted above.

Where a short-circuit develops across but a single coil section of thesecondary winding, an entirely different situation obtains in the fluxpath. By virtue of the short-circuited condition of the one coilsection, a current flows and a back magnetomotive force is developedbythe ow of current from the initial period of the applied potential. Inthe other coil section, however, no current flows and no backmagnetomotive force is developed because the reduced potential appliedto the luminescent tube ordinarily is not sufllcient to establish theglow discharge conditions in the tube. The total back magnetomotiveforce opposing the coursing of flux through core portion I 2 thereforeis only that developed by the current in the one short-circuited coil,that is, about half of that developed under load conditions or fullshort-circuit conditions. This would lead to an excessive flux linkingthe short-circuited coil but for the fact that a shunt path of butone-half the reluctance of that ordinarily encountered is now presented.The main body of flux is shunted around the short-circuited coil over apath including but a single air-gap. For example, upon short-circuitingthe single coil section I5, the main body of ux would be shunted alongthe 4path of core portion Ila, 28a, 28 and lower part of core I2. Thispath includes but the single air-gap GI. It Will be understood that ashort-circuiting of the one coil I6, instead of coil I5, will cause thenur path to se shuntea around that cou section through core rportionIla, 2lb, 28 and the upper part of core piece I2, a path including butthe single air-gap G2. In both cases, the reluctancey of the leakageflux path is less than that where load or full short-circuit conditionsprevail.

Referring now back to my system as a whole,

lit has been pointed out that operation of fluoresbeen employed.

Reference has beenmade to an important object of my invention comprisingthe operation of the tube at comparatively high voltages with the lightemission of the tube being maintained substantiaily constant throughoutthe useful Klife of the tube. 'I'his goal is accomplished by increasingthecurrent capacity of the transformer from.

tially at say 20 milliamperes, at which time its l l to decreasesomewhat the direct shorting eect efiiciency of light emission will b eat a maximum. Regulation of current input is then accomplished in theembodiment of Figures 1 and 2, employing a fixed air-gap, by varying thedimensions of the bridging :blocks 29 or 30 or both. As can best be seenin Figure 2, one or more sections of the secc tional bridging block canbe removed when necessity for increased current 'flow arises.

As a result of this removal, the reluctance of the magnetic by-rpassincreasesv and its shunting action correspondingly diminishes. more fluxcoursing the core leg i2, and more current beingdeveloped in secondarycoil sections Il, Il. This regulatory manipulation can be made at eachtime there is appreciable diminution in the intensity of light emissionfrom tube 21. until the bridging blocks are entirely removed. leavingthe magnetic bypasses with greatest reluctance. At this point the tube21 will operate with required light emission at about 35 to 40 milliiamperes input. The transformer and system are preferably so dimensionedthat the useful life of the tube is ended when more than 40 milliamperesinput is required to produce a satisfactory illumination. Uponoccurrence of further decrease in light emission from the tube, at 40milliampenes input, this tube is discarded and is replaced by a newtube, and the sections of theA bridging block are replaced. i

I prefer to have the magnetic sections of my bridging blocks replaced.by sections of non-magnetic material of the same dimensions when theformer are removed from their containers 31 in adjusting the reluctanceofthe shunt path. By this means I completely fill the containers 31 sothat humming or chatteringv is minimized throughout the various stagesof use of the trans;

former. l

In the illustrated embodiment, the air-gap is bridged on one side only.It is apparent, however, that a more positive result is obtainable bybridging two, three or four sides thereof. Also, the reluctance of theair-gaps Gi and G2 can be varied by adjusting the positions of themagnetic blocks 29 and 30 at diierent distances from the air-gaps. Thiscan be done by suitable mechanical means. If a perfectly constant lightlis desired, a selenium cell may be used to control the mechanical means.

While in the embodiment of Figures 1 and 2, I

have elected to employ a transformer secondary winding consisting of-twosecondary coil sections connected in series, itis equally feasible toemploy but a single secondary coil section for any one secondarywinding. Such'construction I have shown in Figure 3. As illustrated inthat figure, I mount a single secondary coil section IIB on core leg H2.The coil section I i5 is shunted externally thereof by a substantiallyC-shaped magnetic by-pass, having an air-gap Gl. An important feature ofthis construction is that, unlike the embodiment of Figures 1 and 2, thecomponen?I parts of the magnetic by-pass are wholly separate fromthemain core. Thus, the by-pass comprises bar-member 3l and L-shaped member39, both being separate from the core I i2. Since the air-gap G3 betweenthese two members must be fixedv to ensure predictable operation of thetransformer, I find it convenient to fill the airgap with non-magneticmateria1 I0 to maintain the air-gap at its proper value. The material 4lmay, for example, take the form of shims of cardboard, nbre or the like.A membrane lli of nonmagnetic material `-is provided, the purpose ofwhich, just as in the'embodiment of Figure 1, is

of magnetic bridging block |20.

In the embodiment of Figure 4, which is illustrative of another possiblemodification, I combine certain of the features of the examples ofFigures 1 and 3. Here, -:lust as in Figure 1, I mount on the core leg2l2, secondary coil sections 2i5, 2li. Core extension 228 extendscentrally from and at right angles to core leg 2|2 y between said coilsections; and similarly to the of the transformer of Figure l, in thisembodiment I provide separate bar-members di, l2. Between head 228a andmember 4| isv formed airgap G6, while between head4 228b and bar-memberl2 is formed air-gap G5. Since members, 42 are separate from the maincore structure and hence are susceptible to movement relative thereto,proper dimensioning of the fixed airgaps G4 and GI is ensured byinserting non-magnetic and preferably non-metallic spacers 43, 44

in the air-gaps. The magnetic regulatory action 0f the T-shaped coreextension 228, 228a, 22817 is the same as previously described withreference to Fi-gure 1.

As a possible alternative for the use of two bridging blocks, one foreach air-gap to be regulated as in the transformer of Figure 1 in theconstruction illustrated in Figure 4, I employ but a single elongatedmagnetic bridging blocli 4l common to and controlling with equal effectthe air-gaps GI and G5. This bridging block is lam inated and I preferto form it of silicon steel, cast iron or the like. This constructionhas the advantage over that of Figure l of simplicity, easeI ofinstallation, slightly less humming in operation, and ready adjustmentthereof. It is somewhat less sensitive in its control action but I ndthat it may be employed advantageously where some diminution of lightemission may be permitted before correction is required.

In the example of Figure 1, I prefer to form straps 11, 18 of steel oriron. In the construction of Figure 4, Where I provide the strap 211encirclingA the heads 228a, 228D and bar-members 41, 42, I find itadvisable to construct the straps of some suitable non-magneticmaterial. This is done because a paramagnetic metal, such as iron orsteel, would tend to act as a magnetic short or jumper across theair-gaps G4 and G5 thus destroying their regulatory action.

As a further example of an external magnetic by-pass having a fixedair-gap, reference is to be had to Figure 5. In the embodiment therein,secondary coil section 318 is mounted on core leg 312, which at one endabuts in suitable manner core leg 313. One noteworthy feature of theillustrated construction is the provision of cooperating positioningnotches and grooves in the juxtaposed Darts of the transformer core.Thus a notch 46 is formed in core leg 313, to cooperate with and receivea complementary-shaped protuberance 4l in core leg 312. By assemblingthe core parts with their notches and grooves in proper engagement,desired alignment of the several parts is ensured with but a minimum oflabor and effort.

Core leg 312 in Figure 5 is provided as illustrated, with a laterallyand outwardly extending L-shaped extension 48, the outer part 48a ofwhich, being parallel with leg 312, extends to a point just short of leg313 to form a fixed airgap G6 therein of desired dimensions. Thus, asillustrated, the upper end of leg 313, the air-gap G6 and L-shapedextension 48a together form a magnetic by-pass externally shunting theflux and controlling its interlinking with coil section 316. Bridgingblock 330 is provided for spanning the air-gap. It carries out itsregulating action by movement thereof either from left to right inFigure 5, or by movement towards or away from the plane of the paper. Asa possible alternative, it may control the reluctance of the air-gap bybeing moved bodily towards and away from the leg 313 and extension 48a.Its effect is minimized to a desired extent by the interposition of amembrane 331 of non-magnetic material. Because all parts of the coreconstruction oare fixed with respect to each other, the spacers 43, 44of Figure 4, and spacer 40 of Figure 3, may be eliminated in thisexample.

In the embodiments hitherto described, adjustment of the reluctance ofthe magnetic bypass, and hence of the current developed in thetransformer secondary, has been accomplished by bridging a fixedair-gap. It is of course thoroughly practical to construct the magneticbypass so as to have therein a variable air-gap, and to vary the air-gapto producethe desired regulation. Many manners of varying air-gaps willsuggest themselves, and one such possible construction, employing arotor in the air-gap, is illustrated in Figure 6. 'I'herrein a core leg412 has asecondary coil section 415 mountedl thereon, one-half of whichis illustrated. Shunt elements 49, 50 are secured in any desired mannerin abutting relation to leg 412, and extend in parallel manner laterallyand outwardly from core leg 412. These shunt elements 49, 5U are onopposite sides of coil element 415 and thus comprise an external shunt.These elements, moreover, extend outside of casing 431.

Between elements 48, 50 at the free ends thereof, is formed an air-gapGl. Mounted in suitable manner centrally in the air-gap is a rotor. Thisrotor has a hub 51, rotatable about a spindle 52. A handle 53 isprovided, to facilitate manual rotary movement of the rotor. The actionof this handle is purposely made moderately frictional to preventunintentional manipulation of the rotor. A bridging element I4, fast onhub 51, completes the rotor. This rotor has cylindrical surfaces 55, 55,co-axial with spindle 52. The corresponding faces 51, 5l of the shuntelements 48, 5l are also cylindrical and concentric with the surfaces55, 56 to ensure an air-gap Gl of uniform clearance at all points,regardless of the angular position of the rotor.

With the rotor in the full-lined position illustrated, the air-gap is ofminimum reluctance, and the current developed in secondary coil section415 is just sufficient to satisfy the initial requirements of the tubeload, when it is first installed for operation. As the tube ages, andunit light emission falls olf, so that increase of available current isrequired, it is possible to increase the reluctance of the air-gap G1 bychanging the dimensions of the latter. Thus, by manipulating handle 53to turn the rotor slightly, the effective area of the air-gap isdecreased. Or what is magnetically equivalent to the foregoing, theeffective volume of the bridging block is decreased. With the consequentincrease in reluctance of the magnetic by-pass more current is developedin the secondary coil section and the light emission from the tube loadis restored to its initial value. The rotor may be turned to the extremeposition illustrated in dotted lines in Figure 6, at right angles to itsoriginal position at which time the reluctance of the magnetic by-passis at a maximum. The effect of the bypass is at a minimum, and maximumcurrent now flows through the secondary load. I have found that aconstructiony such as described.

while structurally simple and easily adjusted.

possesses the disadvantage of being somewhat noisy in operation.

A further possibility for regulating the airgap of a magnetic by-passinvolving movement of an armature, thereby directly affecting the lengthof the air-gap, is illustrated in Figure 7. Therein, core leg 512, coilsection 515 and casing 532 are depicted. Upstanding shunt elements 61,62 extend laterally and outwardly in parallel relation from leg 512 atright angles thereto and on opposite sides of coil section 515.

Armature 53 is hinged at 04 to element 52 and is provided withprojecting bars 55 which are secured inadjusted position on threadedspindle 66 by suitable means such as nuts 51, 6B. Where desired,othersuitable means may bel employed for adjusting and securing thebridging block in angular position, and the means shown are purely byway of illustration and are not limitations.

In the full-line position of amature 4I. the latter establishes theminimum lengths of airgaps G8 and G9 formed between the armature andelements 61 and 62, respectively.V The lengths of the air-gaps are at aminimum and therefore the reluctance of the shunt path is at a minimum.This corresponds to the condition of initial installation of a. tube inthe systemrequiring minimum current for rated light emission.

Upon an aging of the tube and a decrease in itsv emission of light, agreater ilow oi' current to restore rated conditions is necessary. Thisis had through increasing 4the reluctance of the external magnetic shuntor by-pass. In the illustrated embodiment, this is accomplished byslight readjustment oi amature 83 from the full line position to theangular dotted position, as by manipulation of nuts 61, 68. Thiseiiectively increases the length of the air-gaps thereby decreasing thequantity of flux coursing the shunt pathduring the ignition of the tubeload and consequently increasing the flux linking primary and secondarywindings and increasing the output current.

While in the examples shown I have disclosed the construction only ofmagnetic by-passes disposed externally of the core, it is equallyfeasible, of course, as I have'al'ready suggested, to construct. suchby-passes internally of the core. It is also possible to construct amagnetic bypass in which the air-gap is regulated by sliding, in a ila-tair-gap, a ilat,accurately dimensioned piece of magnetic` material, theposition of the said piece relative to the air-gap determining theeffective bridging of the latter.

A construction combining both these possibilities is illustrated in theshell-type transformer of Figures 8 and 9. In this embodiment the corecomprises main leg 1| on which .primary coil section 3|4 and secondarycoil section SI5 are mounted. Core legs 12, 13, 14, are also provided.Brackets 1B, 11 serve to prevent chattering of the laminations of thevarious core elements. Rivets 18 secure the brackets to the corelaminations. y

The main leg 1| is preferably oriented properly with respect tolegs 12,15 by cooperating notches Aand grooves 3|, l2. Main leg 1| is provided,be-

tween the primary and secondary coil sections H4, BIB, with outwardlyprotruding right-angled extensions 1|a, 1lb, extending on opposite sidesthereof to points just short of legs 13, 14, respectlvely, andrespectively forming therewith the air-gaps GI 0, GII. Bridging members83 and I4 are provided for air-gaps Gill and G|| respectively in orderto increase or decrease the elcacy of the air-gaps, as more particularlypointed out hereinafter.

With ilux coursing momentarily in the direction ot the arrows andassuming that the iiux has not yet built up a voltage in the secondarycoil section IIB sumcient to strike an arc across the tube comprisingthe load, the tlux developed in the primary coil section coursesupwardly through main leg 1|, splitting into two parallel paths in leg12, one oi' these paths extending through leg 1I, the left-hand portionof leg 15 and back up through leg 1|, thereby interlinking coil sectionM5. The other path is through leg 14, the righthand portion oi leg 15and up through main leg 1| to complete the circuit and link coil SI5.

When an arc is struck across the tube load o1 part of main leg 1|, andlinks the secondary winding Il! to insure development of the requiredcurrent.

Similarly, with reversed coursing oi ilux, before the tube is ignited,the ilux courses down leg 1| splitting in two parallel paths at leg 15and thence courses upwardly through legs 13, 14 to leg 12, wheretheparallel paths of flux reunite, to continue their journey to primarycoil section 6|4. Thus, the main body of flux interlinks secondary coilAsection 6|5 beforecurrent begins to ilow in this coil section, but whenthe current is iiowing, it causes a counter magnetomotive force to bedeveloped which bucks the main body of flux. Thereupon, the largerportion oi' the main body of iiux traverses a path down through leg 1|in parallel paths through extensions 1|a, 1lb, up through legs 13, 14and back through leg 12, reuniting at the top of leg 1|. A large portionof the ilux is thereby shunted around the secondary coil section 6|5,and does not interlink this latter.

Now, i! it is desired to increase from time to time the currentdeveloped in the secondary winding, to compensate for decreased unitlight emission in the tube load, this can be accomplished by decreasingthe eiect of the bridging members '33 and 84 provided for the air-gapcontrol, thereby increasing'the reluctance of these latter.

When a fresh tube is initially placed into 0peration, having its highestunit emission, and requiring lowest unit current, it is desired that theeiect of the magnetic'by-passes be at a. maximum. Accordingly, thereluctance interposed by the air-gaps in the magnetic by-passes shouldbe at a minimum. To insure this conthe transformer, current flows incoil section 8|! building 'up a counter magnetomotive force which bucksthe main body of flux. The majorpart of in parallel paths through legs13 and 14, thence across air-gaps GIU and CHI, extensions 1|a,v

1lb, and the two pms reunions m leg 1| to complete the circuit linkingonly the primary dition and with proper design of the constants of theair-gap, the strips 83, 84 will be inserted all the `way across theair-gaps, until they abut stops 85, 86. The strips conveniently aresteadied Y by springs 81 and 38 in order to minimize vibration andchattering. The air-gaps GID, Gli are then substantially completelybridged. Thereafter, upon a decrease in the unit'light emission of thetube load, the strips 83, 84 are pulled out of the air-gaps to a'shortextent, thereby diminishing the bridging action, increasing thereluctance of the magnetic by-passes, and permitting a compensatingamount of current to flow in the secondary load. Y,

It Will be seen from the foregoing -that essentially my inventionresides in the operation of a fluorescent luminous gas discharge tube bya transformer which is regulated so as to provide additional currentupon a falling off of the unit light emission of the tube.

By using high voltages, I am enabled to operate a tube, which, being inone unit, is'several vtimes the length of the largest individual unit.possible in low voltage installations.

ties, depending upon the particular fluorescent salt or salts with whichthe inner wall of the tube is coated. Such a tube is readily produced inany shop equipped to produce the present-day conventional neon signs,employs standard elecwinding lll. Just sumclent ilux courses the lower utrades. and operates with great efliciency and with a high degree ofcoolness as compared with the usual incandescent lamps. Inasmuch as thevisible light emanates from the secondary radiation of the fluorescentsalts, when they are energized by the glow discharge between the`tubeelectrodes, a steady light is produced which is substantially free fromall stroboscopic effects, or objectionableiiicker. Thus, such a lightsource has a widespread scope of utilization in indusn trial, commercialand scientific fields, as well as in household lighting. Such a tube iscapable of operation at comparatively high voltages, say from two tofive thousand volts or more, and as contrasted with known tube equipmentconstructed for use at ordinary household voltages of say 110 or 220volts, is characterized by its simplicity, its small number of parts,its greater efficiency, ruggedness, fiexibiiity and its low first cost.

When such a tube is used in a system employing my new transformer, inaccordance with the new method set forth hereinbefore, there is obtainedfor the rst time a substantially uniform light emission throughout theuseful life of the tube. The life of the tube is greatly increased, andthe desired current regulation is obtained in a simple and inexpensivetransformer. Regulation of the current output of the transformer isobtained in ready and simple manner. Upon discarding a tube at the endof its useful life, even if the glass and metal parts thereof bescrapped, it will be found that because of the long life of the tube,the low rst cost of both the transformer and the tube and the lowoperating cost, the replacement cost, prorated over the life of the tubemeasured in light hours, is extremely low.

To summarize briefly, it may be stated that my new invention ischaracterized, as compared with other high voltage tube operation, byits lower rst cost', lower cost of installation, and lower operatingcosts, all with a useful life at uniform brilliance of more than twicethat of uorescent tube equipment as it is now operated. Contrasted withlow voltage fluorescent tube operation, it has a light emissionefficiency in lumens per watt slightly greater than such construction,has a much greater life, a. lower first cost, produces a steady light bythe use of a simple and inexpensive electrodes and is operated byinexpensive transformer equipment. I nd, for example, that the lcombinedcost of heaters and choke coils employed for proper operation of lowvoltage tube equipment exceeds the cost of the transformer equipmentused according to my invention.

When weighed against available incondescent lighting equipment, my newinvention produces for unit power, from three to four times, up to ashigh as A times, the quantity of light obtainable from iilamentarylamps. Furthermore, it

l possesses the advantage of great exibility makmade of my invention,and as changes may be made in the embodiments hereinbefore set forth. itwill be understood that all matter described herein or shown in theaccompanying drawings is to be interpreted as illustrative and not in alimiting sense.

l. A transformer capable of delivering desired maximum current to itsload, comprising a core; a primary winding and a secondary winding onsaid core; a magnetic by-pass disposed on said core and shunting saidsecondary winding. said by-pass having an air-gap therein; and asectional bridging block for bridging said air-gap, removal or additionof sections to said bridging block determining the effective dimensionsof said air-gap and hence determining the quantity of flux linking saidsecondary winding and the value of the secondary current.

2. In combination, a transformer and a casing of para-magnetic materialfitting snugly about said transformer, said transformer comprising acore, a primary winding and a secondary winding 'on said core, amagnetic by-pass on said y core and shunting said secondary winding andvhaving an air-gap therein, and said casing having a membrane ofnon-magnetic material denning a portion thereof, and adjustable magneticmeans mounted on said casing exteriorly of said membrane for controllingthe flux across the airgap in said magnetic by-pass and thereby deter--mining both the quantity of flux linking said secondary winding and thevalue of the secondposed on said core and shunting said secondarywinding, and means exteriorly of said casing for bridging said air-gapto determine the effective dimensions of said air-gap and hencedetermining the quantity of flux linking said secondary winding and thevalue of the secondary current; and a metal container housing saidair-gap bridging means to ensure against humming of the latter.

4. A transformer capable of delivering desired maximum current to itsload, comprising a core including shunt core means, a primary windingand a secondary winding having a plurality of secondary coil sectionsmounted on the core with said shunt core means extending magneticallyaround individual secondary coil sections and presenting a correspondingplurality of shunt magnetic paths including fixed air-gaps magneticallybetween said coil sections and said primary winding, and means forpresenting a magnetic path 'around all of said fixed air-gaps tosimultaneously determine the effectiveness of each of the same and hencedetermining the quantity of flux linking said primary and secondarywinding coil sections and the value of the secondary current therein.

CHARLES PHILIPPE BOUCHER.

